Italian Language-How to choose the right textbook for adults and children?

I am a teacher of Italian language. For the first time I had a request from a 40 years old man and his 9 years old son to teach them Italian together.
At this point I am not sure what textbook I should choose as there is a big age gap between the two and I am not sure if I should choose a textbook to meet the child's needs or one for adults learners.
Hope you can help,
Arianna

I am a teacher of Italian language. For the first time I had a request from a 40 years old man and his 9 years old son to teach them Italian together.
At this point I am not sure what textbook I should choose as there is a big age gap between the two and I am not sure if I should choose a textbook to meet the child's needs or one for adults learners.
Hope you can help,
Arianna